Tractive apparatus for longitudinally moving elongated material and of the type providing opposed tractive assemblies which grip the interposed material between material gripping bodies circulating in a closed path have long been known. An example of such apparatus is disclosed in Von Eldik U.S. Pat. No. 3,103,306. In prior art apparatus, of which I am aware, each individual material gripping body, or tractive member, was secured to and was part of a link chain trained over sprockets. In such prior apparatus, tractive member movement was effected by application of a driving force to one of the sprockets to thus pull the chains and the attached tractive members against the resistance offered by the gripped material.
Despite the highly efficient material gripping force available in apparatus of the type herein concerned, such prior art devices have not been widely used for the following reasons: First, sprocket drive under heavy loadings at high speed has not been smooth, and second, and most important, chains are formed of many relatively small parts subjected to very heavy stresses when loads and speeds are high. This has resulted in nearly prohibitive maintenance problems in many applications where the apparatus would otherwise be suitable.
The present invention, by confining the tractive members to circulation in a closed path in end-to-end relation and with such members substantially completely filling such path, avoids the previous necessity of interconnecting the members to form a chain. Since the tractive members need not be interconnected, many small, highly stressed and rapidly wearing parts are eliminated to thus provide for long, trouble-free operation.
To effect movement of a group of tractive members through their travel path, a drive pinion is engaged with teeth formed on each tractive member and, since the tractive members are so related to each other that they resist only compressive rather than tensile forces, such tractive members are held in abutting relation about their path by the drive pinion.
These and other advantages will readily become apparent from a study of the following and from the drawings appended hereto, and it is a primary object of this invention to provide new and improved tractive apparatus of the character disclosed.